Provenance of the Upper Cretaceous to upper Eocene clastic sediments of the Western Cordillera of Ecuador: Geodynamic implications

The Late Cretaceous-Eocene clastic deposits of the Western Cordillera of Ecuador record significant changes in the source areas, grain size, and location of the depocenters, related to the accretion of oceanic terranes that constitute the present-day Western Cordillera and Coast. Major changes in the source areas occurred in the ?late Maastrichtian and ?late middle Eocene. They are interpreted as corresponding to the accretion of the Guaranda and Macuchi oceanic terranes, respectively. Major increases in the grain sizes occurred in the ?late Maastrichtian, late Paleocene(?), and ?late middle Eocene, and seem to coincide with the accretion of the Guaranda, Piñón, and Macuchi terranes, respectively. The increasing occurrence of plutonic or metamorphic fragments and the westward shift of the depositional areas through the Paleocene-upper Eocene interval indicate an increasing uplift and erosion of the Cordillera Real. Continuous, although jerky, uplift of the latter during the Maastrichtian-Eocene period, supports the idea that the accreted oceanic material contributed to the crustal thickening and relief creation of the Ecuadorian Andes.